The invention relates to a dryer with recirculated air proportion as well as to a preferred method for its operation.
With regard to the prior art, reference is made to the publication WO 2008/110449 A1, whose disclosure is to be incorporated by reference in its entirety in the present disclosure.
A clothes tumble dryer is generally operated as a vented or condenser dryer. Condenser dryers, whose principle of operation is based on the condensation of the moisture evaporated from the laundry by means of warm process air, require no vent hose and enable energy to be recovered from the heated process air, through use of a heat pump for example. The condensate accumulating in the condenser dryer is collected and either pumped away or disposed of by manual emptying of a collecting vessel. In the case of a vented dryer, on the other hand, the air laden with moisture after passing through a laundry drum is generally ducted out of the dryer. Generally no heat recovery takes place during this process.
Vented dryers having heat recovery are known, however. Thus, for example, the document DE 30 00 865 A1 describes a tumble dryer incorporating heat recovery. The tumble dryer consists of a moving tub which accommodates the laundry and into which there discharges a stream of supply air heated by a heating element, while the moist warm air is ducted as exhaust air by way of an outlet. Disposed in the supply air stream ahead of the heating element is a heat exchanger through which flows the moist warm air from the container.
The energy efficiency of a vented dryer can also be improved by means of an air recirculation system. With this arrangement a fraction of the process air laden with moisture from the laundry in the drying chamber is returned to the drying process by way of the heater. A disadvantage here, however, is that a great deal of the lint originating from the laundry in the drying chamber can reach the heater. This can lead to the buildup of lint in the downstream airways including the heater. The risk of burn marks and the fire hazard are also increased, since the lint may ignite on the heater and find its way into the laundry in the drying chamber. It is likewise disadvantageous that substantially more condensate is produced in the typically long exhaust air duct and more lint is also deposited in the exhaust air duct due to the higher relative humidity of the exhaust air and the process-dependent low volume of the externally ducted process air stream which is routed for example into the room where the appliance is installed.
EP 0 468 573 A1 describes a device for cleaning a heat exchanger of a condenser apparatus in a clothes dryer. In this arrangement the heat exchanger, consisting of a plurality of fins disposed parallel to one another, can be cleaned on its side lying opposite a condensate water tray by means of a cleaning device. The latter contains a reciprocatingly moving, comb-like brush or bristle arrangement to which condensate water contained in the condensate water tray is supplied in addition.
DE 86 05 014 U1 describes a device for automatically cleaning a lint filter which is arranged in a filter housing and retains the lint contained in an air stream directed through the filter housing and the lint filter, wherein the lint filter is movably mounted, there is provided in the filter housing an opening which can be closed by means of a movable cover, the lint filter can be moved into said opening, and devices are present which generate a cleaning air stream through the lint filter from the rear.
DE 10 2005 054 684 A1 describes a device for drying laundry by means of an air stream, the device comprising a drum and a ducting system to direct the current of air, the ducting system having a section which is arranged on the downstream side of the drum, in which the air stream is directed in a downward direction and in which there is disposed a filter for trapping lint from the air stream and associated with said filter is a scraper for scraping off lint trapped by the filter.
DE 694 18 133 T2 relates to a device for cleaning the filter of a hot air stream drying circuit of an electric household appliance comprising a drying compartment. The cleaning device comprises fixed cleaning elements, preferably nozzles, through which water is channeled and which direct a jet of water onto the filter in the opposite direction to the air current flowing through the filter at least during a section of at least one operating phase of the appliance.
EP 1 098 028 B1 relates to a laundry dryer having a self-cleaning lint filter in a drying air duct which has a device for reducing or closing the cross-section of the drying air duct and for generating a jet of air for blowing off lint from the lint filter when the drying air blower is switched on and a device for removing blown-off lint.
DE 100 29 428 A1 describes an air-circulating household appliance comprising a removable and washable filter disposed in the air stream, the filter consisting of a flexible fiber material and being embodied in such a way that it can bind and/or decompose odorous substances.
DE 103 02 864 A1 describes a laundry dryer, in particular a condenser dryer, comprising a rotatably mounted laundry drum which has at least one air inlet and at least one air outlet, and a fan for feeding air into the laundry drum, wherein a switchover device is present for switching the air stream through the laundry drum between recirculated air and exhaust air operation. A filter for trapping lint or other contaminants that are carried out from the laundry drum with the exhaust air can additionally be arranged at the air outlet from the laundry drum.